1. Field
Embodiments relate to a benzimidazole compound, an organic photoelectric device including the same, and a display element including the same.
2. Description of the Related Art
An organic photoelectric device has been highlighted for the next generation display device. The organic photoelectric device may be used in a display element or device driven at a low voltage, and may have various advantages over a thin film transistor-liquid crystal display (TFT-LCD). For example, the organic photoelectric device may be used in a display element or device that may be thinner, may have a wide viewing angle, and may have rapid response speed. A small or medium sized display element or device including an organic photoelectric device may also have an equivalent or better image quality compared to a TFT-LCD, and its manufacturing process may be very simple. Therefore, it is considered that it will be advantageous in terms of cost in the future.
An organic photoelectric device includes an organic light emitting material between a rear plate (including ITO transparent electrode patterns as an anode on a transparent glass substrate) and an upper plate (including a metal electrode as a cathode on a substrate). When a predetermined voltage is applied between the transparent electrode and the metal electrode, current flows through the organic light emitting material to emit light.
Generally, an organic photoelectric device is composed of an anode of a transparent electrode, an organic thin layer as a light emitting region, and a metal electrode (cathode) formed on a glass substrate, in that order. The organic thin layer may include, e.g., an emission layer, a hole injection layer (HIL), a hole transport layer (HTL), an electron transport layer (ETL), and/or an electron injection layer (EIL). It may further include an electron blocking layer or a hole blocking layer due to the emission characteristics of the emission layer.
When an electric field is applied to the organic light emitting diode, the holes and electrons are injected from the anode and the cathode, respectively. The injected holes and electrons are recombined on the emission layer though the hole transport layer (HTL) and the electron transport layer (ETL) to provide light emitting excitons. The provided light emitting excitons produce light by transiting to the ground state.
The light emission layer material may be classified as a fluorescent material using singlet excitons and a phosphorescent material using triplet excitons according to the light emitting mechanism.
When the triplet exciton is transited, it cannot directly transit to the ground state. Therefore, the electron spin is flipped, and then it is transited to the ground state so that it provides a characteristic of extending the lifetime (emission duration) to more than that of fluorescent emission. In other words, the duration of fluorescent emission is extremely short at several nanoseconds, but the duration of phosphorescent emission is relatively long such as at several microseconds.
In addition, evaluating quantum mechanically, when holes injected from the anode are recombined with electrons injected from the cathode to provide light emitting excitons, the singlet and the triplet are produced in a ratio of 1:3, in which the triplet excitons are produced at three times the amount of the singlet excitons in the organic photoelectric device.
Accordingly, the percentage of the singlet exited state is 25% in the case of a fluorescent material, so it has limits in luminous efficiency. On the other hand, in the case of a phosphorescent material, it can utilize 75% of the triplet exited state and 25% of the singlet exited state, so theoretically the internal quantum efficiency can reach 100%. When a phosphorescent light emitting material is used, it has advantages in a luminous efficiency of around four times that of the fluorescent light emitting material.
In the above-mentioned organic photoelectric device, a light emitting colorant (dopant) may be added to an emission layer (host) in order to increase the efficiency and stability in the emission state.